Unusual Guaiane Sesquiterpenoids from Artemisia rupestris

Two new guaiane sesquiterpenoids, (1β,5β)‐1‐hydroxyguaia‐4(15),11(13)‐dieno‐12,5‐lactone (1) and 1,5‐epoxy‐4‐hydroxyguai‐11(13)‐en‐12‐oic acid (2), together with five known compounds, rupestonic acid (3), strobilactone A (4), antiquorin (5), isosclerone (6), and 5‐hydroxy‐2′,3′,4′,7,8‐pentamethoxyflavone (7), were isolated from a 95% EtOH extract of Artemisia rupestris. Compounds 1 and 2 are rare examples of guaiane sesquiterpenoids, incorporating a 12,5‐lactone group or featuring a 1,5‐epoxy ring, respectively. The structures of 1 and 2 were identified by various spectroscopic methods. Compounds 1, 4, and 5 exhibited moderate cytotoxic activities against the human lung cancer 95‐D cell line with IC50 values of 11.3, 19.8, and 34.5 μM, respectively.